1. Field of the Invention
The present invention relates generally to a mobile communication system and method for supporting multimedia services. More particularly, the present invention relates to a system and method for efficiently providing forward broadcast services.
2. Description of the Related Art
A conventional cellular mobile communication system, for example, a mobile communication system based on Code Division Multiple Access 2000 (CDMA2000) High Rate Packet Data (HRPD), supports a unicast service for providing a specific terminal with CDMA data. An address of the specific terminal is designated such that data can be transmitted and received. An access network assigns a frequency band for transmitting data to a corresponding user. However, when the same service data is provided to multiple users, a unicast scheme wastes resources in a network and wireless zone, and increases system load.
FIG. 1 illustrates an example of an Error Control Block (ECB) for providing a broadcasting service in a conventional CDMA system.
Referring to FIG. 1, one ECB includes 16 rows. Each row includes a 125-octet Media Access Control (MAC) packet transmitted from a higher layer. The ECB as illustrated in FIG. 1, is transmitted from a base station to a mobile terminal through a logical channel. In this case, multiple logical channels may be used. Conventionally, one logical channel may be regarded as one broadcast program.
One row of the ECB is 125 octets (that is, 8*125, resulting in 1,000 bits). Moreover, because one row additionally includes 24 overhead bits for transmitting a physical layer packet, 1,024 bits are transmitted as one physical layer packet.
FIG. 2 illustrates a structure for transmitting an ECB as illustrated in FIG. 1. Referring to FIG. 2, one of the columns along the horizontal axis denotes a time slot of high-speed packet data. A physical layer packet is divided and transmitted into two time slots. One time slot is 1.67 ms.
Accordingly, it can be assumed that a logical channel transmits a physical layer packet in two slots at a transmission rate of 307.2 kbps, such that the information of 1,024 bits can be sent.
In FIG. 2, I denotes an interlace index, and interlace indices 0, 1, 2, and 3 are repeated in a time slot unit. One interlace is divided into four multiplexes. In FIG. 2, M denotes a multiplex index.
A transmission structure as shown in FIG. 2 must be set in advance between a base station and a mobile terminal. The transmission structure is determined by mapping tables as shown in Tables 1 and 2.
Table 1 below shows an example of an interlace-multiplex pair mapping table associated with a logical channel.
TABLE 1MultiplexInterlace01230000010———2————3————
As shown in Table 1, a mapping value 0 is assigned to interlace-multiplex pairs (0, 0), (0, 1), (0, 2), (0, 3), and (1, 0). This indicates that Logical Channel 0 is transmitted in the interlace-multiplex pairs. It can be assumed that the other logical channels are transmitted in remaining combinations.
In FIG. 2, it can be found that packets of the ECB are transmitted in time slots based on the interlace-multiplex pairs (0, 0), (0, 1), (0, 2), (0, 3), and (1, 0). A time slot of the interlace-multiplex pair (0, 0) is used twice, such that one packet can be transmitted. A time slot of the interlace-multiplex pair (1, 0) is used four times, such that two packets can be transmitted.
Table 2 below shows length information of an interlace-multiplex pair.
TABLE 2MultiplexInterlace012302222141112111131111
Referring to Table 2, the burst length of the interlace-multiplex pairs (0, 0), (0, 1), (0, 2), and (0, 3) is 2, and the burst length of the interlace-multiplex pair (1, 0) is 4. Because the length of one physical layer packet is 2, one physical layer packet is transmitted in the interlace-multiplex pairs (0, 0), (0, 1), (0, 2), or (0, 3). Two physical layer packets are transmitted in the interlace-multiplex pairs (1, 0). For convenience, it can be assumed that the burst length of the other logical channels is 1.
The base station uses Tables 1 and 2, and sets a transmission interval as illustrated in FIG. 2. Through the transmission interval, packets of the ECB as illustrated in FIG. 1, are multiplexed and sequentially transmitted.
FIG. 3 partially illustrates the format of a conventional broadcast overhead message associated with a logical channel for transmitting a specific Broadcast-Multicast Service (BCMCS) flow. A message field of FIG. 3 may be repeated according to each BCMCS flow identifier (ID).
Referring to FIG. 3, a LogicalChannelSameAsPreviousBCMCSFlow field contains information indicating if a current logical channel on which a current BCMCS flow ID is transmitted, is the same as a previous logical channel on which a previous BCMCS flow ID is transmitted. If the two channels are the same, the LogicalChannelSameAsPreviousBCMCSFlow field is set to 1. Further, since the configuration of the current logical channel is the same as that of the previous logical channel, when the LogicalChannelSameAsPreviousBCMCSFlow field is set to 1, the other fields are omitted. When the configuration of the current logical channel is different from that of the previous logical channel, the LogicalChannelSameAsPreviousBCMCSFlow field is set to 0.
In this case, a PhysicalChannelCount field is set to a value corresponding to the number of interlace-multiplex pairs occupying the logical channel. Each interlace-multiplex pair is indicated by an Interlace field and a Multiplex field. A DataRate field indicates a transmission rate of broadcast data to be transmitted through the logical channel. An OuterCode field indicates an outer coding scheme. A MACPacketPerECBRow field indicates the number of higher layer packets included in one row.
If 99% of the users located within a sector can receive the broadcast service at 307.2 kbps when the conventional CDMA communication system provides a broadcast service, one physical layer packet can be transmitted in two slots. For example, when a time period for transmitting a physical layer packet is doubled, a diversity gain is obtained but a data rate is reduced to half. An HRPD system for transmitting only one packet in one time slot wastes resources by a reduced transmission rate.
When Orthogonal Frequency Division Multiplexing (OFDM) is applied to the HRPD system such that a transmission rate of a broadcast service can increase, 99% of the users located within the sector can receive the broadcast service at 1.2 Mbps. In this case, because a physical layer packet is transmitted in one time slot, there is a problem in that a diversity gain cannot be obtained.
Accordingly, a need exists for an improved system and method capable of simultaneously providing the same broadcasting service to a plurality of users while conserving resources.